■ Overview

This article explores the benefits of using Ethernet direct digital controllers (Ethernet DDCs), also known as building controllers, in building management systems (BMS) and explains how the 10BASE-T1L protocol can fit into a typical BMS architecture.

10BASE-T1L technology features a data rate of 10 Mbps, support for various topologies, and power supply over a single-twisted pair cable, providing seamless Ethernet connectivity for DDC controllers and edge nodes in point-to-point, ring, and line network configurations.

It supports a nearly unlimited number of edge nodes, provides real-time control, and overcomes the limitations of previous protocols.

It is a suitable solution for retrofitting existing BMS as it enables long-distance data transmission of up to 1km and allows reuse of existing single-pair twisted pair cables.

These features facilitate edge-to-cloud connectivity by eliminating the need for power-hungry gateways.

This is for those interested in the latest BMS technology or its potential impact on energy efficiency in buildings. It is a very important resource for them.

■ T1L based DDC

DDC (direct digital controller) systems are essential to modern building management and enable real-time monitoring and control of various building systems.

As technology advances, DDC systems with Ethernet connectivity will become more widespread, further improving building efficiency and safety.

The ADIN1100 PHY, ADIN1110 MAC PHY, and ADIN2111 2-port switch from Analog Devices Inc. (ADI) are ideal solutions for adding 10BASE-T1L technology to DDC systems.

This technology makes building systems easier to manage and maintain by enabling the transmission of process values, configuration information, software updates and diagnostics.

10BASE-T1L technology, which allows the use of long cables up to 1 km in length, has diagnostic functions to quickly and efficiently resolve any faults within the system.

The integration of 10BASE-T1L and software stacks such as Modbus IP and BACnet IP provides a comprehensive solution for industrial automation systems, facilitating efficient data acquisition, device control, and system monitoring.

Figure 1 shows how to integrate 10BASE-T1L products into HVAC (heating, ventilation, and air conditioning) controllers and room controllers for communication with multiple room or building controllers in a ring or line topology.

■Application: T1L-based VAV controller in HVAC systems

○ Definition of VAV
Variable airflow (variA variable air volume (VAV) system is a common HVAC device/controller used in modern office buildings, with multiple systems installed in different zones/areas to maintain indoor temperatures at a comfortable level.

This system allows different zones to operate at different temperatures using the same ventilation system by regulating the amount of air supplied while maintaining a constant temperature.

To ensure adequate ventilation, VAV systems use DDC programming to calculate and command the necessary damper adjustments.

The latest programmable VAV zone controllers include built-in actuators that operate terminal fans and regulate the flow of conditioned air into the space to maintain room temperature.

This controller provides dedicated control for single duct, parallel fan box terminals, and series fan box terminals supporting variable heating capabilities.

The controller consists of two main blocks: a damper actuator and an integrated programmable DDC.

It also supports interfaces to various sensors required to properly adjust wind speed and monitor air quality in VAV applications.

Programmable VAV zone controllers can measure and display zone temperatures, detect occupancy, measure duct temperature, measure exhaust air temperature, measure zone humidity and dew point, detect carbon dioxide (CO₂) levels, and control AV box fan speed.

In large buildings such as airports, 10BASE-T1L controllers can provide optimal energy efficiency and indoor air quality while reducing maintenance and operating costs.


○ Usage examples in large buildings
In this use case, we will focus on a specific area of the airport (Figure 2).

However, it is important to note that the VAV system and control algorithm described here can also be applied to other large buildings.

There are two rooms in this area, and the VAV system uses five sensors and actuators placed at different locations across the ductwork within the same area.

In the first room, two actuators (D1 and D2), one temperature sensor (S1), and one pressure sensor (S2) were used.

S1 and S2 are located in the air supply duct near the terminal, D2 is used as an exhaust damper and D1 is used as an intake damper to control the indoor air flow.

Similarly, the second room uses the same number of sensors and actuators (D3, D4, S3, S4), but due to the added load in the room, a carbon dioxide sensor (S5) and a separate actuator (D5) are added inside the ventilation duct, allowing better control of air flow and air quality.

This VAV control unit monitors and controls sensors and actuators using a control loop algorithm.

Adjust the damper position based on readings from temperature and pressure sensors and then operate it as programmed.

For example, when the temperature changes in room 1, the VAV device starts to open and close dampers D1 and D2, causing a pressure change in the air supply duct, and the change is detected by the pressure sensor (S2).

As the pressure increases, the VAV unit detects the change and adjusts the fan in the air handling unit (AHU) to slow down.<br />
All sensors are connected in a line topology and placed at different locations in the ductwork.

Each damper is directly connected to the VAV unit using a point-to-point topology.

Existing infrastructure structures are severely constrained by limitations on cable length, impedance, thickness, and most importantly, DC loop resistance.

However, to solve these problems, 10BASE-T1L DDC controllers are used to control a network of sensors and actuators in real time over a single twisted pair cable even at distances of 1 km or more.

Additionally, the 10BASE-T1L control device actuator can be used to remotely minimize damper operating time, adjust position to optimal settings, and even evaluate dampers in case of failure.

VAV systems are a powerful tool for maintaining a comfortable environment in large buildings such as airports.

By using sensors and actuators placed in different locations, VAV devices can regulate air flow and air quality to maintain constant temperature and pressure.

With the help of advanced technologies such as 10BASE-T1L DDC controllers, HVAC systems are controlled and maintained more efficiently, contributing to energy savings through improved efficiency.


■ Conclusion

Adding 10BASE-T1L to the building controller improves BMS performance by eliminating the need for complex, high-power gateways and enabling real-time control of sensors and actuators over long distances over a single twisted pair cable.

Building controllers can achieve greater reach using a nearly unlimited number of edge devices, depending on network performance and requirements.

Building controllers that support 10BASE-T1L can monitor network faults and use fault detection and cable diagnostic features to identify cabling problems.

※ About the author
Salem Gharbi is a Systems Applications Engineer in the Sustainable Buildings and Infrastructure business unit at Analog Devices. He has been working in various IoT and industrial applications for 7 years, providing system-level solutions focused on industrial automation.